Did your son's teacher or school provide any specific requirements for the science project assignment? For instance, is your son allowed to do a demonstration or model project, or does he have to select a project that includes a problem, hypothesis, experiment and conclusion? Before he gets started, you might ask your son's teacher about this particular project idea (to confirm whether or not it meets the school's requirements).

For general information about the scientific method and what makes a good science project, check out the Helping Your Child With Science Fair Projects info center:
http://www.education.com/topic/help-child-with-science-fair-projects/

Good luck!